1. Field
The following description relates to wireless communication and, more particularly, to an apparatus and method for performing handover in a multiple component carrier system.
2. Discussion of the Background
Cellular communication is a concept that has been introduced to overcome the restriction of a service area and the restriction of frequency and subscriber capacity. Cellular communication includes a method for providing coverage by changing a single high-output base station into a plurality of low-output base stations. That is, a mobile communication service area is divided into several small cells, different frequencies are allocated to neighboring cells, and the same frequency band is used by two cells which are sufficiently spaced apart from each other, thus not having interference therebetween, so that the frequency can be spatially reused.
Handover refers to a function in which, if a user equipment exits a current communication service area (hereinafter referred to as a ‘serving cell’) and moves to a neighboring communication service area (hereinafter referred to as a ‘neighbor cell’), the user equipment is tuned with a new traffic channel of the neighbor cell, thus continuously maintaining a traffic state. A user equipment communicating with a specific base station (hereinafter referred to as a ‘source base station (BS)’ is linked to another neighbor base station (hereinafter referred to as a ‘target BS’) through handover if the intensity of a signal in the source base station becomes weak. When handover is performed, a problem, such as call disconnection occurring when a user equipment moves from one cell to a neighbor cell, can be solved.
In general, a wireless communication system uses one bandwidth for data transmission. For example, the 2nd generation wireless communication system uses a bandwidth of 200 KHz to 1.25 MHz, and the 3rd generation wireless communication system uses a bandwidth of 5 MHz to 10 MHz. In order to support an increasing transmission capacity, the bandwidth of a recent 3GPP LTE or 802.16m has extended to 20 MHz or higher. To increase the bandwidth may be considered indispensable so as to increase the transmission capacity, but to support a high bandwidth even when the quality of service required is low may generate great power consumption.
In order to solve such problem, there has emerged a multiple component carrier system in which a component carrier having one bandwidth and the center frequency are defined, and data is transmitted or received through a plurality of component carriers using a wide band. That is, a narrow band and a wide band are supported at the same time by using one or more component carriers. For example, if one component carrier corresponds to a bandwidth of 5 MHz, a bandwidth of a maximum 20 MHz can be supported by using four component carriers.
However, in a handover in a base station using a single component carrier, the base station only performs the handover by taking only a single cell, measured and reported by a user equipment, into consideration. In case of a multiple component carrier system, however, the handover procedure must be performed by taking multiple component carriers into consideration. To this end, a target base station has to configure component carriers necessary for a user equipment through the handover procedure and has to provide a quality of service to the degree that a source base station provided the quality of service to the user equipment. In this case, it is difficult to configure an adequate level of component carriers or appropriate component carriers because the target base station may not accurately determine the quality of service was provided to the user equipment before the handover. Accordingly, there is a need for an apparatus and method for performing handover by taking multiple component carriers into consideration.